In short:
- OpenJDK has multiple meanings and can refer to:
- free and open source implementation of the Java Platform, Standard Edition (Java SE)
- open source repository — the Java source code aka OpenJDK project
- prebuilt OpenJDK binaries maintained by Oracle
- prebuilt OpenJDK binaries maintained by the OpenJDK community
- AdoptOpenJDK — prebuilt OpenJDK binaries maintained by community (open source licensed)
Explanation:
Prebuilt OpenJDK (or distribution) — binaries, built from http://hg.openjdk.java.net/, provided as an archive or installer, offered for various platforms, with a possible support contract.
OpenJDK, the source repository (also called OpenJDK project) – is a Mercurial-based open source repository, hosted at http://hg.openjdk.java.net. The Java source code. The vast majority of Java features (from the VM and the core libraries to the compiler) are based solely on this source repository. Oracle have an alternate fork of this.
OpenJDK, the distribution (see the list of providers below) – is free as in beer and kind of free as in speech, but, you do not get to call Oracle if you have problems with it. There is no support contract. Furthermore, Oracle will only release updates to any OpenJDK (the distribution) version if that release is the most recent Java release, including LTS (long-term support) releases. The day Oracle releases OpenJDK (the distribution) version 12.0, even if there’s a security issue with OpenJDK (the distribution) version 11.0, Oracle will not release an update for 11.0. Maintained solely by Oracle.
Some OpenJDK projects – such as OpenJDK 8 and OpenJDK 11 – are maintained by the OpenJDK community and provide releases for some OpenJDK versions for some platforms. The community members have taken responsibility for releasing fixes for security vulnerabilities in these OpenJDK versions.
AdoptOpenJDK, the distribution is very similar to Oracle’s OpenJDK distribution (in that it is free, and it is a build produced by compiling the sources from the OpenJDK source repository). AdoptOpenJDK as an entity will not be backporting patches, i.e. there won’t be an AdoptOpenJDK ‘fork/version’ that is materially different from upstream (except for some build script patches for things like Win32 support). Meaning, if members of the community (Oracle or others, but not AdoptOpenJDK as an entity) backport security fixes to updates of OpenJDK LTS versions, then AdoptOpenJDK will provide builds for those. Maintained by OpenJDK community.
OracleJDK – is yet another distribution. Starting with JDK12 there will be no free version of OracleJDK. Oracle’s JDK distribution offering is intended for commercial support. You pay for this, but then you get to rely on Oracle for support. Unlike Oracle’s OpenJDK offering, OracleJDK comes with longer support for LTS versions. As a developer you can get a free license for personal/development use only of this particular JDK, but that’s mostly a red herring, as ‘just the binary’ is basically the same as the OpenJDK binary. I guess it means you can download security-patched versions of LTS JDKs from Oracle’s websites as long as you promise not to use them commercially.
Note. It may be best to call the OpenJDK builds by Oracle the “Oracle OpenJDK builds”.
Donald Smith, Java product manager at Oracle writes:
Ideally, we would simply refer to all Oracle JDK builds as the “Oracle JDK”, either under the GPL or the commercial license, depending on your situation. However, for historical reasons, while the small remaining differences exist, we will refer to them separately as Oracle’s OpenJDK builds and the Oracle JDK.
OpenJDK Providers and Comparison
---------------------------------------------------------------------------------------- | Provider | Free Builds | Free Binary | Extended | Commercial | Permissive | | | from Source | Distributions | Updates | Support | License | |--------------------------------------------------------------------------------------| | AdoptOpenJDK | Yes | Yes | Yes | No | Yes | | Amazon – Corretto | Yes | Yes | Yes | No | Yes | | Azul Zulu | No | Yes | Yes | Yes | Yes | | BellSoft Liberica | No | Yes | Yes | Yes | Yes | | IBM | No | No | Yes | Yes | Yes | | jClarity | No | No | Yes | Yes | Yes | | OpenJDK | Yes | Yes | Yes | No | Yes | | Oracle JDK | No | Yes | No** | Yes | No | | Oracle OpenJDK | Yes | Yes | No | No | Yes | | ojdkbuild | Yes | Yes | No | No | Yes | | RedHat | Yes | Yes | Yes | Yes | Yes | | SapMachine | Yes | Yes | Yes | Yes | Yes | ----------------------------------------------------------------------------------------
Free Builds from Source – the distribution source code is publicly available and one can assemble its own build
Free Binary Distributions – the distribution binaries are publicly available for download and usage
Extended Updates – aka LTS (long-term support) – Public Updates beyond the 6-month release lifecycle
Commercial Support – some providers offer extended updates and customer support to paying customers, e.g. Oracle JDK (support details)
Permissive License – the distribution license is non-protective, e.g. Apache 2.0
Which Java Distribution Should I Use?
In the Sun/Oracle days, it was usually Sun/Oracle producing the proprietary downstream JDK distributions based on OpenJDK sources. Recently, Oracle had decided to do their own proprietary builds only with the commercial support attached. They graciously publish the OpenJDK builds as well on their https://jdk.java.net/ site.
What is happening starting JDK 11 is the shift from single-vendor (Oracle) mindset to the mindset where you select a provider that gives you a distribution for the product, under the conditions you like: platforms they build for, frequency and promptness of releases, how support is structured, etc. If you don’t trust any of existing vendors, you can even build OpenJDK yourself.
Each build of OpenJDK is usually made from the same original upstream source repository (OpenJDK “the project”). However each build is quite unique – $free or commercial, branded or unbranded, pure or bundled (e.g., BellSoft Liberica JDK offers bundled JavaFX, which was removed from Oracle builds starting JDK 11).
If no environment (e.g., Linux) and/or license requirement defines specific distribution and if you want the most standard JDK build, then probably the best option is to use OpenJDK by Oracle or AdoptOpenJDK.
Additional information
Time to look beyond Oracle’s JDK by Stephen Colebourne
Java Is Still Free by Java Champions community (published on September 17, 2018)
Java is Still Free 2.0.0 by Java Champions community (published on March 3, 2019)
Aleksey Shipilev about JDK updates interview by Opsian (published on June 27, 2019)
